Within months she went from full-figured to fabulous and now Kim Kardashian is sharing her secret with the world.

In a tweet she sent out Sunday, the Keeping Up With the Kardashians star revealed her old school diet plan which was designed in the 1950s and is high in protein, low in carbs.

'I've actually been doing the Atkins diet & luv it,' she confessed.

Now and then: Kim Kardashian (left) on Thursday leaving Ruth Chris' Steak House in Woodland Hills and (right) pregnant in April, tweeted she's lost weight thanks to The Atkins Diet

A 60 year old plan: Dr. Robert C. Atkins developed his high protein, low carb diet in 1953

'She is eating lots of lean proteins,
healthy fats like nuts and avocado, carbs, fruits, veggies and cheese,' a
rep for Atkins says.

'She
wanted to be a healthy, nursing mom and not toxify her milk with her
diet or lose weight too quickly. She's been doing Atkins since her
doctor approved it at the end of June.'

Rihanna and Sharon Osbourne have also tried the diet.

The reality star - who UsWeekly reported in August has lost 30 pounds since delivering her baby - was criticized on
tabloid covers in the spring for ballooning up to 200 pounds while she was pregnant
with Kanye West's baby North, born in June.

In March she addressed all the weight talk on Extra.

'There are maybe two or three covers just this week that say I am 200 pounds,' she said.

'I'm
like, "You are 60 pounds off here."'

Hold the bread! The reality star looked svelte on Saturday while leaving Casa Vega in the Sherman Oaks area of LA

Thankfully, she hasn't lost all the weight: The Honey fragrance queen shows off her enviable curves as she puts North in the back seat of her car while leaving the Mexican restaurant

'It wouldn't even bother me if I
gained all the weight,' she adds.

'And I have the biggest sweet tooth and I love
junk food. Being pregnant, I don't like any of it.'

During her pregnancy she said she stuck to carrots and celery with ranch dressing, not Big Macs.

'I'm
waiting for the moments when someone's like let's go to McDonald's and
Taco Bell - that's not happening for me and I'm kind of sad about it,'
she said in the spring.

As
far as her changing body she said, 'I'm not going to lie and be like,
"Oh, it's been amazing and I've adjusted great." At the beginning it was
tough for me when your body changes so much… but once you kind of grasp
that and embrace it it's amazing.'

Her more daring post-pregnancy looks: At the West Hollywood DASH store on Friday (left) and in Paris on October 1 (right)

In March, when she was heavily pregnant, she posted a photo of herself from Dancing With The Stars on Instagram and lamented about her thin days of yore.

The LA native was also thin during the beginning of her pregnancy in December 2012 when she posed in a flesh-toned bikini in Florida.

Kim's slim down doesn't only have to do with dieting.

The 32-year-old has reportedly been working out every day since she had North in June. She has been spotted several times in her gym clothes, even when she was taking in Fashion Week in Paris last month.

She has been working out with trainer Tracy Anderson, who got Gwyneth Paltrow into killer shape.

In September the gym owner said of Kim: 'She's a gorgeous woman. I think the reason why the weight is coming off is because she's very connected.'

She added, 'I went and met little North and Kim's really taking it in stride. She's really connected to the baby, which is what's important. She's focused on the baby and nursing and taking her time.'

One hot mama in a two piece: The Drop Dead Diva actress models a bikini in Florida in December when she was several weeks along with her child